Kaposi's sarcoma- and B cell lymphoma-associated human herpesvirus 8 (HHV-8) specifies particular proteins that are believed to contribute to angioproliferative and malignant pathogenesis. Key among these is the interleukin-6 homologue, vIL-6, which via its signal transducing properties promotes angiogenesis, cell proliferation and cell survival. The expression of vIL-6 is maximal during lytic, productive replication, but we have demonstrated that it is also expressed as a bone fide latent protein in primary effusion lymphoma (PEL) cells, and, coupled with its predominant intracellular localization, acts in an autocrine manner via ER-initiated intracellular signaling to support PEL growth and survival. Other latency functions of vIL-6, mediated from the ER compartment, may be operative. Unpublished data from this laboratory have established that depletion of latently expressed vIL-6 in PEL cells leads to increased RTA expression and to lytic reactivation, suggesting a role of vIL-6 in regulation of latent-lytic switching. During chemically-induced lytic reactivation, we have found that vIL-6 is a negative regulator of virus production in both endothelial and PEL cells. The present application will focus on the molecular basis of vIL-6 retention and signaling within the ER compartment and the mechanisms and roles of vIL-6 function in relation to virus biology, in part by utilizing the unique reagents and knowledge that we have acquired from our previous studies of vIL-6. The three aims will examine: (1) the roles of ER proteins calnexin and VKORC1 in vIL-6 localization and activity; (2) ER-localized signaling and functions of vIL-6; (3) the role of vIL-6 in the regulation of latent-lytic switching and productive replication. These areas of study are novel and, we believe, of considerable value to future development of anti-viral and therapeutic strategies.